1. Field of the Invention
The present invention relates to a microwave oven having a stationary wave magnetic field detecting device.
2. Description of the Prior Art
Generally, a microwave oven cooks food by using microwaves, and the intensity of the microwaves generated from a magnetron of the microwave oven is varied in accordance with characteristics of the cooked food. That is, various factors of the food such as material, shape, etc. of the food determine microwave absorption and the magnitude of microwave energy. Accordingly, the microwave oven usually performs the cooking operation after analyzing the status of the food by various sensors.
FIG. 1 schematically shows a magnetic fluid detecting device of a conventional microwave oven.
As shown in FIG. 1, the conventional microwave oven includes a magnetron MGT for generating microwaves of approximately 2450 MHz, a waveguide 10 for transmitting the microwaves generated from the magnetron MGT into a food 11 in a cooking chamber 2, and a magnetic field detecting device 100 for detecting the cooking status of the food 11 by receiving electromagnetic waves reflected through the waveguide 10.
The magnetic field detecting device 100 includes an antenna sensor 101, a diode D, and a shield member 120. The antenna sensor 101, the diode D, and the shield member 120 are fixed on a wall of the waveguide 10, in a manner that the antenna sensor 101 is protruded inside the waveguide 10.
The diode D is connected with an end of the antenna sensor 101, to apply the detected voltage of the stationary wave received from the antenna sensor 101 to a microcomputer 130, and the microcomputer 130 determines the cooking status of the food 11 by the detected voltage of the stationary wave received through the diode D.
FIG. 2 is a view for explaining the operating principle of a conventional magnetic field detecting device. As shown in FIG. 2, the end of the antenna sensor 101 is grounded on an inner wall of the waveguide 10 by welding, and has 0 (zero) degree of electric potential, while another end of the antenna sensor 101 is connected with the diode D through an inserting hole 10a of the waveguide 10.
Further, in order to have a predetermined sectional area A between the waveguide 10 and the antenna sensor 101, a certain portion of the antenna sensor 101 forms a semicircular loop. Through the predetermined sectional area A formed in the loop of the antenna sensor 101, a magnetic flux, which is formed by the stationary wave reflected into the waveguide, passes.
Meanwhile, the microwaves generated from the magnetron MGT are radiated in the form of an electromagnetic wave, and the combination of the microwaves advancing into the cooking chamber 2 from the waveguide 10, and the microwaves reflected from the cooking chamber 2 into the waveguide 10 forms the stationary wave in the waveguide 10.
Here, the voltage is induced from the antenna sensor 101 as follows: When the magnetic flux formed by the stationary wave in the waveguide 10 passes through a predetermined sectional area A formed between the waveguide 10 and the antenna sensor 101, the magnetic flux density B generated in the loop in the antenna sensor 101 is obtained by the following formula 1: EQU B=/A (1)
Further, the electromagnetic wave is a function of time, and the magnetic flux density B induced at the sectional area A in the antenna sensor 101 is accordingly varied in magnitude in accordance with the time. Accordingly, by the Maxwell equation, the voltage induced to the antenna sensor 101 can be obtained by the following formula 2: EQU E=-dB/dt (2)
FIG. 3 shows a voltage switching section of the magnetic field detecting device shown in FIG. 1. As shown in FIG. 3, an anode of the diode D is connected to the antenna sensor 101, and a cathode of the diode D is connected with an electrolytic capacitor C being connected in parallel relation with a resistor R, forming a closed circuit.
The diode D detects the voltage in accordance with the stationary wave of the antenna sensor 101, and the electrolytic capacitor C smooths the detected voltage into a predetermined voltage which is outputted as an output voltage Vout by a voltage drop generated at both ends of the resistor R.
By employing the magnetic field detecting device having such an antenna sensor, the conventional microwave is enabled to adjust to the various cooking environments which are varied in accordance with the shape or material of the food when cooking the food, so that the detection error of the sensor is reduced and the cooking status of the food is precisely detected.
The antenna sensor of the magnetic field detecting device employed in the conventional microwave oven, however, has a problem as follows. As shown in FIG. 2, one end of the antenna sensor is grounded on the inner wall of the waveguide by welding, while the other end thereof is connected with the diode, the electrolytic capacitor and the resistor, respectively, by being extended outside the waveguide, to be connected with an input wire. Accordingly, various processes such as a process of fixing the antenna sensor, a process of connecting respective circuit elements to the antenna sensor, etc., need to be performed repetitiously. As a result, the working process becomes complicated, disturbing the automation or mass-production of the microwave oven, and deteriorating the productivity.
Further, in the microwave oven having the conventional magnetic field detecting device, the antenna sensor fixing locations can not be precisely controlled with respect to the waveguide, so that there are uneven sectional areas formed in the loops of the antenna sensors, and the exact voltage value can not be detected by the antenna sensor.
Further, the fixed portion of the antenna sensor fixed on the wall of the waveguide by welding is chemically deformed or snapped off by the long and repetitious use thereof, resulting in a deteriorated reliability about the detected stationary wave data.